It is estimated that at least 1.7 billion barrels of heavy crude oil (also called bitumen) are present in the tar sands of Northern Alberta, in Canada. Tar sands are mixtures of natural origin of sand and/or clay, of water and of oils which are extremely dense and viscous. This bitumen extracted from these tar sands is viscous and solid, or semi-solid, and is difficult to transport since it does not flow easily at temperatures normally encountered in an oil pipeline. Despite these transportation difficulties and the extraction costs, tar sands are widely exploited.
There are various methods for extracting bitumen. Mention may in particular be made of:                Mining extraction, where, in an open cast mine, the bitumen is recovered by digger-loaders and transported in trucks.        CSS (Cyclic Steam Stimulation), which consists in using the same well alternating between steam injection and bitumen extraction. The steam liquefies the bitumen and makes pumping possible. The extraction is carried out via injection-pause-production cycles.        SAGD (Steam Assisted Gravity Drainage), which uses horizontal wells combined in pairs. The upper well constantly injects steam, while the lower well collects the water and the bitumen.        In situ combustion of the bitumen, which consists in burning the bitumen underground in order to liquefy it and to pump it (THAI process).        
In the process by mining extraction, the sand containing the bitumen is milled before being subjected to a conditioning step, called hydro-transport, which initiates the release of the bitumen. In practice, the milled ore is mixed with hot water, generally containing additives such as sodium hydroxide, complexing agents, etc, to create a suspension also referred to as a “slurry”, which is then pumped in a pipeline to a processing plant.
In the processing plant, at least one primary separation step is carried out, consisting of a step of flotation by injection of air into the medium.
The primary separation step makes it possible to obtain 3 phases:                the flotation froth, at the surface of the cell, which contains the majority of the bitumen,        the middle phase which comprises the rest of the bitumen attached to the inorganic particles which are difficult to separate,        the bottom, which mainly comprises sand which separates rapidly.        
The flotation froth is recovered in order to extract the bitumen therefrom. The middle phase is subjected to a subsequent solid-particle concentration step. The bottom is processed so as to ultimately end up as solid waste.
The objective of the technologies used during the steps for separating the bitumen from its sand is to recover the maximum amount of bitumen in the froth, and to minimize the bitumen residues attached to the inorganic particles both in the middle phase and in the bottom. It is also necessary to limit the amount of particles in the froth which impair the subsequent processing operations.
Those skilled in the art are aware of certain technologies which make it possible to aid the recovery of bitumen during these various steps.
U.S. Pat. No. 4,425,227 uses a light oil, such as kerosene or diesel fuel, as bitumen collector and froth formation aid.
U.S. Pat. No. 4,946,597 claims a process using methyl isobutyl carbinol as conditioning agent for enhancing bitumen flotation. U.S. Pat. No. 7,931,800 describes the use of Ca(OH)2 for reducing the affinity between clay particles and bitumen, thus facilitating the adsorption of bitumen droplets onto air bubbles during the flotation step and resulting in better bitumen recovery yields.
Several patents describe the use of chemical products which have surfactant properties and are capable of facilitating bitumen release from tar sands. For example, patent CA 1293464 describes the combination of a surfactant with a polyethylene oxide in order to increase bitumen recovery yields. Patents AU 2008240334 and US 20090090658 claim the use of proteins or lipids, respectively, and also of chemically modified derivatives thereof with a view to the same results. Patent US 20110114539 reports the use of lignin-based amphiphilic derivatives. Patent U.S. Pat. No. 7,691,260 uses block copolymers composed of an acrylic acid-based hydrophilic part and of a vinyl acetate-based hydrophobic part. Patent US 20100193404 proposes the use of surfactant molecules comprising a phosphate ester function, an aromatic nucleus and a poly(ethylene oxide) oligomer segment).
Patent US 20050194292 describes a method for enhancing the recovery of bitumen from tar sands by adding an agent, an acrylamide-based, anionic water-soluble polymer, capable of sequestering cations. The bitumen is brought into contact with the agent before or during the primary separation of the bitumen and the mineral matter. In a similar perspective, patent WO 2011/130109 uses a combination (i) of a cationic polymer (coagulant) and (ii) of an anionic polymer (dispersant) capable of precipitating clay particles in suspension during the flotation step, thus reducing the solid content in the flotation froth and enhancing bitumen extraction yields.
The pH of the medium during the flotation step is conventionally adjusted to about 8-9 with sodium hydroxide. Patents CA 2768522 and WO 2012/088430 claim complete or partial replacement of the sodium hydroxide via the addition, respectively, of metal (Na or K) carboxylate salts or of cement.
The prior art proposes varied chemistries which, however, are not efficient enough in the face of fine particles. The processing of oxidized or nonoxidized ores, which contain significant concentrations of fines, results in poor froth quality and can potentially impair or prevent subsequent processing operations. Furthermore, some processes use products which are very dangerous to handle.